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Technical Bulletin 2/14
THE SNMP PROTOCOL
The SIMPLE NETWORK MANAGEMENT
PROTOCOL, SNMP is a widely used
management protocol that operates on top of
IP and UDP protocols. In the basic mode of
operation the SNMP is a Request / Response
protocol. The requesting, controlling process is
called the Manager and the process
responsible for providing the responses is
called the Agent. In the SATELLAR use case,
the SATELLAR modem will act as a SNMP
Agent and the monitoring PC or SCADA would
be the SNMP Manager.
THE SNMP REQUEST
SNMP requests can be either Get or Set type.
The Get request queries for a value of the
parameter from the managed device and the
Set writes a new value for the parameter.
The requested parameters are identified with
OID (Object Identifier). For example, the value
for the device temperature would be identified
by the OID: 1.3.6.1.4.1.30306.1.1.1.4.2.1.1.0 .
MIB
Mappings between OID numbers and
parameters are stored in a tree formatted
hierarchical database called Management
Information Base, MIB. To enable SNMP query
of a certain parameter, both the Manager and
the Agent must have respective OID available
in their MIB. For SATELLAR-2DS/20DS modem,
the MIB database contents for SATELLAR related
parameters are available for download at
SATEL web pages. After download, they can be
installed or imported to the Manager MIB.
SIMPLE NETWORK MANAGEMENT PROTOCOL
SATELLAR MANAGEMENT WITH SNMP GET AND SET
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The following drawing illustrates the SNMP Get
operation in more detail. The SCADA system has
been configured to periodically monitor the
temperature of the SATELLAR modems in the
network. The SCADA system has a MIB entry
stored for the SATELLAR specific parameter, so the
SCADA will be able to map the temperature
parameter to the correct OID. This OID is then
included in the request. When the request is
received by the SATELLAR, it will map the OID to
the requested parameter of temperature. The
internal logic in the SATELLAR reads the
temperature value and sends it in the SNMP
response back to SCADA. Again, in the response
the identifier for the requested parameter is the
OID. The monitored SATELLAR device can be
either locally connected or remote modem behind
the IP radio interface. The SATELLAR network must
be configured to operate in the Packet Mode.
However, if it is sufficient to monitor only locally
connected modem, radio protocol mode can be
selected freely.
SCADA SUPPORT
Many SCADA solutions have a built-in support
for the SNMP. Also, many SCADA providers
recommend SNMP usage by adding a protocol
gateway to the system. The protocol gateway
will convert the SCADA supported protocol to
SNMP queries and vice versa. For example ABB
Microscada supports the SNMP operation via
the SNMP-OPC (Open Connectivity via Open
Standards) gateway. See the following drawing
for the illustration for the gateway operation.
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The OPC gateway
mediates and
translates the OPC-
SNMP communication.
In this case, the MIB
resides at the OPC
Gateway, instead of
SCADA.
SCADA
SATELLAR Packet Mode
(IP operation) required.
For local monitoring,
the radio protocol
mode can be selected
Monitored device
can be any SNMP
enabled device with
Agent functionality.
SNMP GET OPERATION